1. Field of the Invention
The present invention relates to an AC-DC converting device and an electrical apparatus, and more particularly to a technology of converting an alternate current (AC) to a direct current (DC).
2. Description of the Related Art
In order to eliminate adverse effects of conducted noise propagating from an electronic device connected to a commercial power source to other electronic device or the like via an alternate current (AC) cable, various standards such as the standard proposed by the CISPR (International Special Committee on Radio Interference) are provided to suppress the conducted noise. Most of the conducted noise results from a switching regulator. A general approach of suppressing the conducted noise is to provide a filter constituted of a coil, a capacitor or a like element between an AC input end of a power source, and a switching regulator. Conducted noise greatly fluctuates depending on an operation state of the electronic device. Normally, a filter which meets the requirements on standard limit value defined by the standard in all the possible operation states of the electronic device is used so that the conducted noise may not exceed the standard limit value in all the possible operation states of the electronic device.
Japanese Patent No. 3583267 recites an image forming apparatus that enables to optimally control the number of voltage fluctuations resulting from an in-rush current into a heater in various states of the image forming apparatus, and to suppress power source voltage fluctuation and higher harmonic wave to a commercial power source without additionally providing a hardware component or a filter member.
Power consumption of a filter differs depending on the filtering performance. In other words, a filter having a high filtering performance consumes a large amount of electric power. Accordingly, in use of a filter which meets the requirements on standard limit value in all the possible operation states of an electronic device, a larger amount of electric power than required may be consumed if the conducted noise is lower than the standard limit value. Also, the above publication is silent about a technique of filtering the conducted noise.